The energy requirements for batteries are continually increasing, while constraints on volume and mass continue to be present. Further, the demand for safe, low cost and environmentally friendly materials is increasing. These demands and battery specifications cannot be met using traditional lithium-ion battery chemistries. Although lithium-ion batteries have long been optimized and have demonstrated stable energies, these systems are limited by the amount of lithium that can be reversibly inserted and removed from the battery's active material structure.
The requirements for greater performance, safety, low cost and environmentally friendly materials can only be achieved through the development of new battery materials. Researchers have proposed the replacement of the carbon-based anode with tin. Tin alloys with lithium during the charging of the battery. The lithium-tin alloy forms a maximum concentration of 4.4 lithium atoms per tin atom, a concentration which equals a capacity of 993 mAh/g. A traditional carbon-based anode has a theoretical capacity of 372 mAh/g. Therefore, the replacement of traditional carbon-based anode batteries with tin-based anode batteries could result in higher energy capabilities.
Research has demonstrated that there are two main issues with the use of a tin-based anode. The first is a poor cycle life and the second is a poor utilization of the tin. A poor cycle life is defined as poor retention of battery energy as a function of the number of charge-discharge cycles. Researchers have taken two approaches to solving these problems. First, by forming an intermetallic compound of tin and at least one other metal, and second, by adding a non-electrochemically active material to the anode composite. However, the prior research has failed to address the fundamental causes of the poor performance of lithium-tin batteries, which are: 1) a large volume expansion of the tin-lithium particles resulting from the alloying of lithium with tin on charge; and 2) the breaking apart of tin agglomerates during the above-stated volume expansion. The volume expansion results in separation of the tin particles from the matrix during subsequent cycles and breaking of tin agglomerates results in fine particles with exposed fresh surface area. This fresh surface area is not in contact with the matrix, and thus like the separation of tin particles from the matrix, results in decrease in battery capacity. Therefore, there is a need for a lithium-tin battery that exhibits adequate cycle life and proper utilization of the tin.